California Aquatic Invasive Species (AIS)
University of California
California Aquatic Invasive Species (AIS)

Invasive Seaweeds and Hull Fouling Species

Devil Weed

Scientific Name

Sargassum horneri Visit algaeBASE for full scientific classification. 



  • Annual brown algae, up to about 15 feet long.
  • Small, fern-like leaf blades on wiry "stems" with many small air bladders.
  • Forms very dense groves.
  • Occurs in the intertidal zone and down to depths of 100 feet.
Invasion Pathways and Distribution
  • Native to warm seas in Japan and Korea.
  • Extensive natural dispersal capabilities via drifting fragments.
  • Can spread by attaching to vessel hulls or by drifting.
  • Invasive in Baja California, Mexico, southern California, and the California Channel Islands.
  • First reported in California in 2003.
Life History
  • Capable of self-fertilization.
  • Young plants grow from embryos released from numerous, conspicuous, chili pepper-shaped reproductive structures.
  • Completes its life cycle in approximately one year.
  • Spreads quickly.
  • Areas in southern California currently dominated by this species that thrives in warm water conditions.
  • Competes with natives for space and light.
References and Useful Links

For references by category and links to other useful AIS sites see our LEARN MORE page.

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